Resistance Spot Welding Two-Step Current Control
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Solution Overview
Problem
Resistance spot welding methods fail to consistently produce a nugget of appropriate diameter due to electrode wear and disturbances, such as nearby existing welds, leading to reduced current density and potential splashing, especially when the heat generation pattern deviates from the target pattern.
Innovation Solution
A method involving two-step current patterns during both test and actual welding, where the first step current secures the current path and the second step achieves the desired nugget diameter, with adaptive control adjusting the current passage to match the cumulative heat generation to the target value, ensuring a stable nugget formation without increasing welding time or causing splashing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the same welding current is applied after electrode wear expands the contact area, then the welding process is simple and fast, but the current density decreases and nugget diameter reduces
Solution Approach 1:
The welding current is made dynamic by dividing it into multiple steps with different current values. The first step uses a higher current to quickly establish the current path, while the second step uses a lower current to complete nugget formation. This dynamic current adjustment compensates for electrode wear effects and maintains consistent nugget quality throughout production.
Solution Approach 2:
The welding current is segmented into two distinct steps: a first step with current Ia to secure the current path, and a second step with current Ib to achieve the desired nugget diameter. This segmentation allows each step to optimize for its specific function, maintaining nugget quality despite electrode wear.
2Manufacturing precision
If a high welding current is set in advance to compensate for current diversion to existing welds, then the nugget diameter is sufficient, but heat generation near the electrode becomes excessive causing splashing
Solution Approach 1:
The welding current is divided into two steps with different magnitudes. The first step uses current Ia (where 0.05 ≤ Ia/Ib ≤ 0.5) to initially secure the current path without generating excessive heat. The second step then applies the higher current Ib to achieve the required nugget diameter. This segmentation prevents the splashing that would occur with a single high current applied from the start.
Solution Approach 2:
The first current step Ia performs a preliminary action to secure the current path between the steel sheets before the main nugget formation current Ib is applied. This preliminary current path establishment ensures that when the higher current is applied in the second step, the heat is generated primarily at the nugget location rather than near the electrode surface, preventing splashing.
3Manufacturing precision
If a predetermined pattern for changing welding current is used to compensate for electrode wear, then the nugget diameter can be maintained, but extensive testing is required to derive appropriate patterns for numerous conditions
Solution Approach 1:
The invention changes the parameter of welding current from a single predetermined value to a two-step variable pattern. By establishing universal ratios for the first step current Ia relative to the second step current Ib (0.05 ≤ Ia/Ib ≤ 0.5), the system achieves adaptability to various welding conditions without requiring extensive condition-specific testing and pattern derivation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively maintains a good nugget diameter under various conditions, including electrode wear and disturbances, preventing splashing and ensuring consistent weld quality without extending welding time.
Implementation Method 1
A point-like weld is obtained using the resistance heat generated by passing the high welding current
Implementation Method 2
a pair of electrodes squeezing the steel sheets from above and below
Data Source
Figure 1(A)~1(B)
Figure 2(A)~2(B)
Figure 3(A)~3(B)
AI summary
In a resistance spot welding method, test welding and actual welding in which a current pattern is divided into two or more steps are performed. In the test welding, a constant current of a different value is passed in each step, and a time variation of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume are stored as a target value. In the subsequent actual welding, when a time variation amount of an instantaneous amount of heat generated per unit volume deviates during any step from the results of the test welding, a current passage amount is controlled to compensate for the difference during a remaining welding time in the step. In the test welding, 0.3 x Ix ≤ Ia < Ix, where Ia is the current in the first step, and Ix is the current in second and subsequent steps.